The modulated spraying nozzle control (MSNC) system equipped with pulse-width modulation (PWM) nozzle is a new kind of variable rate technology (VRT) for spraying. A design-scheme of the electronic control unit（ECU）was investigated for the PWM nozzle, which included a communication unit that could transmit messages between the computer and the ECU in the tractor, and the control unit which might improve the response speed by using the cross-current chop-wave circuit. Using EDA tools, the simulation and the experiment were carried out to study the circuit. The results show that with this unit the rising edge of the circuit is 4.5 ms and the falling edge is 9 ms. Furthermore, the relationship between flow rate and duty cycle is linear.